All subdivision and land development activities
involving an increase in impervious cover (i.e., reduction in permeability)
shall be conducted in conformance with the following standards:
A. After installation of impervious cover, peak discharges
for the one-, ten-, twenty-five-, and one-hundred-year frequency storms
from the site shall not exceed the respective peak discharge performance
standards in Appendix A, Section VI.
B. Stormwater runoff shall be managed so that no downstream
increases in flood damages or impairment of streets and other public
facilities occur. The Municipal Engineer may require that downstream
impacts be evaluated at critical locations such as dams, tributaries,
existing developments, undersized culverts, and floodprone areas.
The municipality and its Engineer shall make the final determination
with respect to the degree of management required for any site. The
applicant shall evaluate the effects of the proposed plan on such
critical locations by providing computed water surface elevations
(WSEL) for the ten- and one-hundred-year storms. Methods of computation
shall have prior approval of the Municipal Engineer. At such downstream
critical locations, stormwater management may be exercised by:
(1) Providing off-site improvements to downstream conveyances
in order to contain flow increases.
(2) Providing downstream drainage easements with sufficient
widths to contain the flood limits.
C. Groundwater recharge and water quality for regulated
earth disturbance activities.
[Amended 3-22-2005 by Ord. No. 311]
(1) No regulated earth disturbance activities within the
municipality shall commence until approval by the municipality of
a plan which demonstrates compliance with state water quality requirements
after construction is complete. Appendix D provides the procedure
for determining groundwater recharge and water quality requirements.
(2) Maximizing the groundwater recharge capacity of the
area being developed is required.
(3) The BMPs must be designed to protect and maintain
existing uses (e.g., drinking water use; cold water fishery use) and
maintain the level of water quality necessary to protect those uses
in all streams, and to protect and maintain water quality in "Special
Protection" streams, as required by statewide regulations at 25 Pa.
Code Chapter 93 (collectively referred to herein as "state water quality
requirements").
(4) To control post-construction stormwater impacts from
regulated earth disturbance activities, state water quality requirements
can be met by BMPs, including site design, which provide for replication
of pre-construction stormwater infiltration and runoff conditions,
so that post-construction stormwater discharges do not degrade the
physical, chemical or biological characteristics of the receiving
waters. As described in the DEP Comprehensive Stormwater Management
Policy (#392-0300-002, September 28, 2002), this may be achieved by
the following:
(a)
Infiltration: replication of pre-construction
stormwater infiltration conditions;
(b)
Treatment: use of water quality treatment BMPs
to ensure filtering out of chemical and physical pollutants from the
stormwater runoff; and
(c)
Streambank and streambed protection: management
of volume and rate of post-construction stormwater discharges to prevent
physical degradation of receiving waters (e.g., from scouring and
erosion).
(5) DEP has regulations that require municipalities to
ensure design, implementation and maintenance of best management practices
("BMPs") that control runoff from new development and redevelopment
(hereinafter "development") after regulated earth disturbance activities
are complete. These requirements include the need to implement post-construction
stormwater BMPs with assurance of long-term operations and maintenance
of those BMPs.
(6) Evidence of any necessary permit(s) for regulated
earth disturbance activities from the appropriate DEP regional office
or County Conservation District must be provided to the municipality.
D. In establishing the watershed conditions for calculating
stormwater runoff prior to development, the following assumptions
shall apply:
(1) Woodland or meadow in good condition shall be used
for all undeveloped areas.
(2) Average antecedent moisture conditions as defined
by the Natural Resource Conservation Service.
(3) Drainage area reductions equal to the area of undrained
depressions or pond factor adjustments in accordance with the Urban
Hydrology for Small Watersheds, Technical Release No. 55 (TR-55, USDA,
NRCS) procedure shall be applied in determining predevelopment peak
discharges from Karst geologic areas.
E. Hydrologic methods. All plans and designs for stormwater
management facilities shall be reviewed by the Municipal Engineer.
Plans for facilities other than storm sewers should determine stormwater
peak discharge and stormwater runoff by the use of the Soil Cover
Complex Method as set forth in TR-55, and Technical Release No. 20
(TR-20) with specific attention given to antecedent moisture conditions,
flood routing, and peak discharge specifications included therein
and in the National Engineering Handbook, Section 4, both by U.S.
Department of Agriculture, Natural Resource Conservation Service.
The Municipal Engineer may permit the use of the Modified Rational
Method or other methods for calculation of the storage capacity of
a stormwater management facility from drainage areas of 20 acres or
less.
(1) Coefficients. Acceptable runoff coefficient values
for use in the Rational Method equation, and permissible curve numbers
for TR 55, maximum velocities, and suggested roughness coefficients
and permissible velocities for channels are identified in Tables A-2
through A-5 of Appendix A, Section I of this chapter. When applying the Rational Method coefficients in Table
A-3, open space coefficients shall be used for undeveloped, densely
vegetated (nonforest) areas instead of meadow coefficients.
(2) The Rational Method may be used in lieu of the Soil
Cover Complex Method to compute design flows for the sizing of storm
sewers, inlets, and swales. Methods approved by the Pennsylvania Department
of Transportation and/or Department of Environmental Protection may
be used to design the waterway areas of bridges.
(3) Rainfall amounts for the return periods specified
shall be determined using the Pennsylvania Department of Transportation
Intensity Duration Frequency Curves presented in Figure A-1 of Appendix
A, Section Iof this chapter. Rainfall duration for hydrograph generation shall be selected
for the specified recurrence intervals on the basis of twice the computed
time of concentration for the given watershed and subwatersheds. In
no case shall the duration be less than one hour.
(4) Time of concentration shall be determined in accordance
with the method presented in TR-55.
(5) In order to reduce stormwater runoff volumes from
developed areas and encourage groundwater recharge, underground basin
drains, infiltration trenches, and cisterns are permitted, to which
roof leaders may be connected. These drains consist of stone-filled
basins which temporarily store and release water below ground surface.
Plans for such facilities shall be submitted to the municipality for
approval, and the basins shall be used only in those areas where soils,
geologic, and water table conditions permit. Performance criteria
which govern the location, design, construction, and maintenance of
these infiltration facilities are contained in Appendix A, Section
IV of this chapter. Suggested guidelines are contained in Standards and Specifications
for Infiltration Practices (MD DNR).
F. Stormwater management facilities and related installations
shall be provided:
(1) To permit unimpeded flow of natural watercourses.
Such flow may be redirected as required, subject to the approval of
the Pennsylvania Department of Environmental Protection and the municipality.
(2) To insure adequate drainage of all low points along
the curbline of streets.
(3) To intercept stormwater runoff along streets at intervals
reasonably related to the extent and grade of the area drained, and
to prevent substantial flow of water across intersections or flooded
intersections during storms, in accordance with the procedures contained
in the Pennsylvania Department of Transportation Design Manual Part
2, DM-2, Chapter 10 (PennDOT).
(4) To insure adequate and unimpeded flow of stormwater
under driveways in, near, or across natural watercourses or drainage
swales. Suitable pipes or other waterways shall be provided as necessary.
(5) To properly drain stormwater runoff from all land
development projects. All lot and open areas shall be designed to
drain to the nearest practical street or drainage system, existing
or proposed, as defined by the Municipal Engineer, with no impact
on adjoining properties, unless an area specifically designed for
stormwater detention is provided.
G. Storm sewers and related installations:
(1) Storm sewers, where required by zoning and land use
densities, shall be placed under or immediately adjacent to the roadway
side of the curb, or as directed by the municipality, when parallel
to the street within the right-of-way.
(a)
When located in undedicated land, they shall
be placed within a drainage easement not less than twenty-feet wide
as approved by the Municipal Engineer.
(b)
The use of properly designed, graded, and turfed
drainage swales is encouraged in lieu of storm sewers in commercial
and industrial areas and, where approved by the Municipal Engineer,
in residential areas. Such swales shall be designed not only to carry
the required discharge without excessive erosion but also to increase
the time of concentration, reduce the peak discharge and velocity,
and permit the water to percolate into the soil, where appropriate.
Criteria related to the use and design of drainage swales are contained
in Appendix A, Section II of this chapter.
(2) The design capacity of storm sewers shall be in accordance
with Urban Drainage Design Manual, Hydraulic Engineering Circular
Number 22 (US DOT, FHA). Storm drainage systems shall be designed
without surcharging inlets to provide conveyance of stormwater runoff
into a detention basin or similar facility utilized to manage the
rate of stormwater runoff. To avoid surcharging inlets, and to ensure
that inlets will receive stormwater runoff, the hydraulic grade line
at the inlet should be at least six inches below the elevation of
the inlet grate. Where site grading will direct stormwater runoff
from the one-hundred-year design storm to a detention basin or similar
facility utilized to manage the rate of stormwater runoff, then the
storm sewer may be designed for the ten-year-design storm. Where site
grading will not direct stormwater runoff from the one-hundred-year
design storm to a detention basin or similar facility utilized to
manage the rate of stormwater runoff, then the storm sewer shall be
designed for the one-hundred-year-design storm. Conveyance of storms
to the detention basin, up to and including the one-hundred-year frequency,
shall be provided so as not to endanger life or seriously damage property.
(3) Storm inlet types and inlet assemblies shall conform
to the Pennsylvania Department of Transportation Standards for Roadway
Construction as approved by the Municipal Engineer.
(a)
Inlets shall, at a minimum, be located at the
lowest point of street intersections, to intercept the stormwater
before it reaches pedestrian crossings, or at sag points of vertical
curves in the street alignment which provide a natural point of ponding
of surface stormwater.
(b)
Where the municipality deems it necessary because
of special land requirements, special inlets may be approved.
(c)
The interval between inlets collecting stormwater
runoff shall be determined in accordance with the Pennsylvania Department
of Transportation Design Manual Part 2, DM-2, Chapter 10, Section
5, Capacity of Waterway Areas, or Urban Drainage Design Manual (HEC-22,
US DOT, FHA).
(d)
In curbed sections, the maximum encroachment
of water on the roadway pavement shall not exceed 1/2 of a through-traffic
lane or one inch less than the depth of curb during the ten-year design
storm of five-minute duration. Inlets shall be provided to limit the
encroachment of water on the pavement. When inlets are used in a storm
system within the right-of-way limits of a street in lieu of manholes,
the spacing of such inlets shall not exceed the maximum distance of
450 feet.
(e)
The design of storm inlets shall be in accordance
with Drainage of Highway Pavements, Hydraulic Engineering Circular
Number 12, (US DOT, FHA).
(4) Accessible drainage structures shall be located on
a continuous storm sewer system at all vertical dislocations, at all
locations where a transition in storm sewer pipe sizing is required,
at all vertical and horizontal angle points exceeding 5°, and
at all points of convergence of two or more influent storm sewer mains.
The construction locations of accessible drainage structures shall
be as indicated on the subdivision drainage plan or area drainage
plan approved by the municipality.
(5) When evidence available to the municipality indicates that existing storm sewers have sufficient capacity as determined by hydrograph summation and are accessible, proposed stormwater facilities may connect to the existing storm sewers so long as the peak rate of discharge does not exceed the amount permitted by §
183-12A of this article.
H. Bridges and culverts shall have ample waterway to
carry expected flows, based on the following minimum storm frequencies:
ten-year for driveways; twenty-five-year for local streets; fifty-year
for collector streets; and one-hundred-year for arterials; or as required
by the Municipal Engineer. Bridge and/or culvert construction shall
be in accordance with the Pennsylvania Department of Transportation
specifications.
(1) The design criteria contained in this article are
intended for use in conjunction with the Chapter 105 Regulations of
the Pennsylvania Department of Environmental Protection entitled,
“Water Obstructions and Encroachments.” All information
and regulations contained in Chapter 105 shall be considered to be
incorporated into this article as if reproduced in full.
(2) A PA DEP permit in accordance with Chapter 105 shall
be required for any obstruction or encroachment in the regulated waters
of the commonwealth, prior to the approval of the stormwater plan.
All areas of the municipality shall be classified as rural, suburban,
or urban, as determined by the Municipal Engineer (See PA DEP § 105.161)
for bridge and culvert designs. In the event any question or conflict
arises between this article and the PA DEP Chapter 105 Regulations,
the design criteria contained in the PA DEP regulations shall govern.
(3) Refer to Appendix A, Section II, of this chapter for additional design criteria.
I. Detention or retention basins for the management of
stormwater peak discharges shall meet the following requirements:
(1) Basins shall be installed prior to or concurrent with
any earthmoving or land disturbances which they will serve. The phasing
of their construction shall be noted in the narrative and on the plan.
(2) The design of all facilities over limestone formations
shall include measures to prevent groundwater contamination and, where
required, sinkhole formation. Soils used for the construction of basins
shall have moderate-to-low erodibility factors (i.e., “K”
factors of 0.32 or less).
(3) Energy dissipators and/or level spreaders shall be
installed at points where pipes or drainageways discharge to or from
basins. Generally, outlet pipes designed to carry the predevelopment,
one-year storm flow will be permitted to discharge to a stream with
only an energy dissipator; discharges to drainage swales shall be
spread with a level spreader or piped to an acceptable point of discharge
downstream.
(4) Outlet structures within detention/retention basins
shall incorporate childproof, nonclogging trash racks or grates over
all horizontally oriented openings. All vertically oriented openings
over 12 inches, or larger in any dimension, where entry by a child
could cause injury or death, shall be covered with childproof, nonclogging
trash racks, except where such openings carry perennial stream flows.
Design openings less than six inches in any dimension shall be covered
with a pipe screen (e.g., Neenah R-7512 or equivalent). Measures to
completely drain detention/retention basins in the event of clogging
of the primary design opening(s) shall be incorporated into the design
of basin outlet structures. Basin outlet pipes shall have a minimum
inside diameter of 15 inches or a cross-sectional area of 176 square
inches, except that pipes under a twenty-five foot or greater fill
shall not be less than 24 inches or a cross-sectional area of 453
square inches, and shall consist of reinforced concrete.
(5) Outlet aprons shall be designed and shall extend at
a minimum to the toe of the basin slope. Where spillways will be used
to manage peak discharges in excess of the ten-year storm, such spillways
shall be constructed to withstand the pressures of impounded waters
and convey flows at computed outlet velocities without erosion.
(6) Stormwater detention facilities shall be designed
to release their total volumes detained within the following maximum
time periods:
(a)
Roofs and parking lots: 24 hours.
(b)
Detention basin: 48 hours.
(c)
Infiltration facilities: 72 hours.
(7) When the Pennsylvania Department of Environmental
Protection requires facilities to be permitted, the designer shall
submit all information to the PA DEP regional office, and obtain all
necessary approvals and permits pursuant to Pennsylvania Code, Title
25, Chapter 105, Darn Safety and Encroachment Act.
(8) Downstream analysis:
(a)
Where deemed necessary by the Municipal Engineer,
the applicant shall submit an analysis of the impacts of detained
stormwater flows on downstream areas within the watershed, established
with the concurrence of the Municipal Engineer. The analysis shall
include hydrologic and hydraulic calculations necessary to determine
the impact of peak discharge modifications of the proposed development
on critical locations such as dams, tributaries, existing developments,
undersized culverts, and floodprone areas.
(b)
Review and comment on the analysis by the Engineer
of a downstream municipality shall be obtained as deemed necessary.
(9) Detention basins may be waived by the municipality, upon recommendation of the Municipal Engineer, at sites in close proximity to larger receiving streams, depending on the hydrology of the watershed. This is to facilitate drainage prior to main stream flooding. It shall be incumbent upon the applicant to demonstrate that no downstream increase in stream flooding or channel erosion will result in accordance with §
183-12I(8) of this article, and that no increases in peak discharge within the receiving stream will occur as outlined under §
183-12A of this article.
(10)
Multiple-use basins. The design and construction
of multiple-use stormwater detention facilities are strongly encouraged.
In addition to stormwater management, where appropriate, facilities
should allow for recreational uses, including ballfields, play areas,
picnic grounds, etc. Provision for parking facilities within basins
and permanent wet ponds with stormwater management capabilities may
also be appropriate. Prior approval and consultation with the municipality
are required before design. Multiple-use basins should be constructed
so that potentially dangerous conditions are not created.
(11)
Multiple-development basins. Stormwater management
facilities designed to serve more than one property or development
in the same watershed are encouraged. Staged construction of existing
or proposed multiple-use detention facilities by several developers
in conjunction with watershed development is encouraged. Each developer
shall be responsible for the incremental increase in stormwater runoff
generated by the respective development and incremental construction
improvements necessary for the overall detention facility. Prior approval
and consultation with the municipality is required before design of
such facilities.
(12)
Alternative detention facilities. Alternative
stormwater detention facilities including rooftop, subsurface basins
or tanks and in-pipe detention storage, or other approved alternative
designs are permitted as determined by the Municipal Engineer.
(13)
Specific criteria related to the design of detention
basins is contained in Appendix A, Section III of this chapter.
J. All calculations shall be submitted to the Municipal
Engineer on computation sheets for approval. If the Municipal Engineer
determines through review and independent computation that the size(s)
of storm pipes or detention basins is insufficient, the municipality
may require the developer to increase the size(s) of said storm pipes
or detention basins. If the storm drainage system design is completed
on a computer installation, sufficient supporting data shall be provided
to allow comprehensive review by municipal officials.
K. When the elevation of any existing or proposed entrance
to a structure, including windows, is lower than the elevation of
the public cartway serving that site, a grading plan shall be submitted,
reviewed and approved as part of the zoning permit process for the
proposed structure.
L. Natural drainageways shall be utilized to the maximum extent possible in carrying stormwater runoff, provided such use remains consistent with the purpose of this chapter specified in Article
I, §
183-3 of this chapter.
M. Stormwater management facilities located outside of
existing or proposed rights-of-way shall be located within and accessible
by easements as follows:
(1) Drainage easements.
(a)
Where a tract is traversed by a watercourse, drainageway, channel or stream, there shall be provided a drainage easement paralleling the line of such watercourse, drainageway, channel or stream. The width of the drainage easement will be adequate to preserve the unimpeded flow of natural drainage in the one-hundred-year floodplain, in accordance with computed top widths for water surface elevations determined under Subsection
A of this article.
(b)
Drainage easements shall provide for maintenance,
and for the purpose of widening, deepening, improving or protecting
such drainage facilities.
(2) Access easements. Where proposed stormwater management
facilities are not adjacent to proposed or existing public rights-of-way
or are not accessible due to physical constraints, as determined by
the Municipal Engineer, a twenty-foot-wide passable access easement
specifying rights of entry shall be provided. Access easements shall
provide for vehicle ingress and egress on grades of less than 10%
for carrying out inspection or maintenance activities.
(3) Maintenance easements. A maintenance easement shall
be provided which encompasses the stormwater facility and appurtenances
and provides for access for maintenance purposes. The maintenance
easement must be located at least 20 feet outside of the one-hundred-year
surface elevation and the stormwater facility and appurtenances.
(4) Easements shall stipulate that no trees, shrubs, structures,
excavation, or fill be placed, and no regrading be performed within
the area of the easement without written approval from the municipality
upon review by the Municipal Engineer. Upon approval of the Municipal
Engineer, such landscaping may be placed in maintenance easements,
provided it does not impede access.
(5) Whenever practicable, easements shall be parallel
with and linked to property lines of the subdivision.
(6) All easement agreements shall be recorded with a reference
to the recorded easement indicated on the site plan. The format and
content of the easement agreement shall be reviewed and approved by
the Municipal Engineer and Solicitor.
[Amended 3-22-2005 by Ord. No. 311]
A. No regulated earth disturbance activities within the
municipality shall commence until approval by the municipality of
an erosion and sediment control plan for construction activities.
B. An erosion and sediment control plan for construction
activities shall be submitted to the municipality for any land developments,
nonregulated earth disturbance of 5,000 square feet or more, and regulated
earth disturbance activities. DEP has regulations that require an
erosion and sediment control plan for any earth disturbance activity
of 5,000 square feet or more, under 25 Pa. Code § 102.4(b).
C. In addition, under 25 Pa. Code Chapter 92, a DEP “NPDES
Construction Activities” permit is required for regulated earth
disturbance activities.
D. Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office or County Conservation District must be provided to the municipality. The issuance of an NPDES Construction Permit [or permit coverage under the statewide General Permit (PAG-2)] satisfies the requirements of Subsection
A above.
E. A copy of the erosion and sediment control plan and
any required permit, as required by DEP regulations, shall be available
at the project site at all times.
Compliance with the provisions of this chapter
shall be in accordance with the following additional general criteria:
A. Materials workmanship and methods. All materials,
workmanship, and methods of work shall comply with the Pennsylvania
Department of Transportation Publication 408 specifications, as accepted
and commonly used by the municipality, and shall be considered to
be incorporated into this article as if copied in full. In the event
a conflict arises between the requirements of this article and the
PennDOT Publication 408 specifications, the Municipal Engineer shall
resolve the difference, and said opinion shall be binding.
B. Record (as-built) drawings. At the completion of the
project, and as a prerequisite for the release of the guarantee or
issuance of an occupancy permit, the owner(s) or his representative
shall:
(1) Provide a certification of completion from a registered
professional verifying that all permanent facilities have been constructed
according to the plans and specifications and approved revisions thereto.
(2) Provide a set of approved stormwater management plan
drawings showing all approved revisions and elevations and inverts
to all manholes, inlets, pipes, and stormwater management facilities.
C. The municipality shall inspect stormwater management
facilities to ensure proper functioning of such stormwater management
facilities. These inspections shall occur at least once annually for
five years after the installation of said stormwater management facilities,
and then at least once every three years thereafter. The municipality
shall also inspect stormwater management facilities after a one-hundred-year-or-greater
storm event.
D. If the municipality determines at any time that any permanent stormwater management facility has been eliminated, altered, or improperly maintained, the Loyalsock Township shall advise the responsible party of required corrective measures and shall provide said responsible party with a specific time frame to implement the required corrective measures. If such action is not taken by the property owner, the municipality may cause the work to be done and backcharge all costs to the property owners in accordance with Article
IV of this chapter.
E. Supplemental standards and criteria contained in the
technical reference materials listed in Appendix B of this chapter are hereby incorporated into this chapter to govern the
hydrologic and hydraulic design provisions contained herein.